One of the common causes of downtime with MySQL is running out of
connections. Have you ever seen this error? “ERROR 1040 (00000):
Too many connections.” If you’re working with MySQL long enough
you surely have. This is quite a nasty error as it might cause
complete downtime… transient errors with successful transactions
mixed with failing ones as well as only some processes stopping
to run properly causing various kinds of effects if not monitored
properly.

There are number of causes for running out of connections, the
most common ones involving when the Web/App server is creating
unexpectedly large numbers of connections due to a
miss-configuration or some script/application leaking connections
or creating too many connections in error.

The solution I see some people employ is just to increase
max_connections to some very high number so
MySQL “never” runs out of connections. This however can cause …

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